Hydroquinone (or 1,4-dihydroxybenzene) has many uses. Many of the uses are associated with hydroquinone's action as a reducing agent that is soluble in water. For example, hydroquinone is used as a developing agent in black-and-white photography, lithography, and x-ray films. It is also used as an intermediate to produce antioxidants for rubber and food. Furthermore, it is added to a number of industrial monomers to inhibit polymerization during shipping, storage, and processing. As a polymerization inhibitor, hydroquinone prevents polymerization of acrylic acid, methyl methacrylate, cyanoacrylate, and other monomers that are susceptible to radical-initiated polymerization.
Hydroquinone can undergo mild oxidation to convert to the compound parabenzoquinone, C6H4O2, often called p-quinone or simply quinone. Reduction of quinone reverses this reaction back to hydroquinone. Some biochemical compounds in nature have this sort of hydroquinone or quinone section in their structures, such as Coenzyme Q, and can undergo similar redox interconversions.
In human medicine, hydroquinone is sometimes used topically for skin whitening and/or to reduce the color of skin. Hydroquinone is sometimes combined with alpha hydroxy acids that exfoliate the skin to quicken the lightening process. There are several disadvantages of existing hydroquinone manufacturing process, such as low selectivity; highly polluted waste stream; high reaction temperature and energy cost.